1. Field of the Invention
The present invention relates to high voltage circuit interrupters or reclosers and in particular to a time delayed, spring biased, auxiliary undervoltage lockout mechanism.
2. Background of the Invention
Reclosers, or circuit interrupters, are inserted into power lines to protect a power distribution system. Most faults on power distribution lines are of a momentary nature and of sufficient magnitude to blow fuses if current allowed to be conducted to the fuses. When a fuse does blow in a power distribution system, it is necessary to send a person to change it which is time consuming an expensive. The function of a circuit interrupter is to automatically reenergize power distribution after a momentary fault such as an overcurrent condition or ground fault.
In operation, the circuit interrupter senses the peak value of the current conducted and interrupts its flow by opening or tripping contacts before fuses can blow or equipment can be damaged. After an interval the recloser closes, restoring power to the system, and it remains closed until the next fault is sensed. If the fault was temporary in nature, such a branch momentarily falling against a line, the circuit interrupter will remain closed and the system energized. If the fault remains on the system, the circuit interrupter will again trip open and reclose after a period of time.
Some faults are of a more permanent nature such as those caused by a line falling to the ground. As a consequence, reclosers are built so that they will only trip a limited number of times within a short duration before locking open. Were this not done a recloser would cycle until failure and many of the fuses to be protected would blow anyway. Typically a recloser will allow two shots or trip operations to follow a fast time current characteristic and two additional shots along a somewhat slower time current characteristic before locking open or out.
Reclosers or circuit interrupters are usually self-contained units taking operating energy directly from the system. To effect the reclosing operation, a solenoid powered by line voltage is energized to reclose the main contacts. A problem is sometimes encountered when a low voltage condition occurs on a line such that the contacts energizing the solenoid are closed but voltage on the line is insufficient to reclose the main contacts. In this condition, the solenoid remains energized, but does not reclose the contacts which would de-energize the solenoid. Since the solenoids are designed to be energized only for a short period of time, the solenoids will heat up and fail. This necessitates repair or replacement of the recloser which is both time-consuming and expensive.